The present invention relates to the manufacture of semiconductor devices. More particularly, the present invention relates to improved techniques for metallic etching and stripping remaining photoresist and residual sidewall passivation.
In the manufacture of certain types of semiconductor devices, such as a semiconductor device that uses aluminum interconnects, a metallic layer such as aluminum or titanium is etched in a metal etching device leaving residual sidewall passivation and remaining photoresist.
To facilitate discussion, FIG. 1 is a schematic view of a prior art etch tool 10, which comprises a load lock 12, a metal etch chamber 14, a strip chamber 16, and a cooling station 18.
A semiconductor wafer, which has a metallic layer disposed below an etch mask (such as a photoresist mask or hardmask), is placed in the load lock 12, which allows the semiconductor wafer to enter the etch tool 10 while maintaining a vacuum in the etch tool 10. In this example, the etch mask is a photoresist mask. From the load lock 12 the wafer is transferred to the metal etch chamber 14, which is dedicated to providing a metal etch. Such etching chambers, such as reactive ion etch chambers, typically generate a plasma to allow etching. The etch chamber 14, for example, uses Cl2 and BCl3 (boron trichloride) as the etchant gases during the metal etch. Additives such as N2, or CHF3 may also be added depending upon the nature of the etching.
In some prior art reactive ion metal etch chambers 14, an electrode adjacent to the wafer is biased to create a potential across the wafer to electrostatically attract the plasma to the wafer, which enhances etching. Such etch chambers also tend to have interior pressures on the order of 1 to 20 millitorr (mT). The plasma etches away parts of the metallic layer not protected by the etch mask to form metallic interconnections. The etching process creates residual sidewall passivation formed from redeposited etch products.
The semiconductor wafer may then be transferred from the etch chamber 14 to the strip chamber 16. The strip chamber 16 may be a downstream plasma device, which generates a plasma remotely from the wafer and subjects the semiconductor wafer to ions generated from the plasma. The strip chamber 16 also tends to operate at pressures on the order of 1 torr, which is generally much higher than the pressure in the metal etch chamber 14. The strip chamber 16 removes the photoresist mask. In the prior art, some strip chambers also provide corrosion passivation by exposing the wafer to a water vapor plasma to provide corrosion protection.
FIG. 2 is a cross-sectional view of part of a semiconductor wafer 22, which forms a substrate, after an aluminum layer has been etched to form aluminum interconnects 23 and after the semiconductor wafer 22 has been subjected to an etch mask strip and corrosion passivation. Redeposited etched metal residue is deposited on the sides of the aluminum interconnects 23 and the photoresist mask to form residual sidewall passivation 25. For aluminum interconnects, the residual sidewall passivation may be formed from redeposited etch residue, which may be aluminum in the form of a chloride or fluoride. When the aluminum residue is exposed to oxygen, aluminum oxide is formed, which tends to be difficult to remove in a conventional strip chamber. After the photoresist mask is stripped, part of the residual sidewall passivation 25 that was adjacent to the photoresist mask may remain, forming “bat ears” 26. In other processes, the “bat ears” may be so thin that they fall over forming “veils”.
Because the residual sidewall passivation 25 is significantly composed of inorganic material such as aluminum or titanium, the strip chamber 16 may not, in many cases, be able to remove the residual sidewall passivation 25.
The semiconductor wafer 22 may then be transferred from the strip chamber 16 to the cooling station 18, where the semiconductor wafer 22 is cooled. The semiconductor wafer 22 may then be transferred from the cooling station 18 back to the load lock 12, so that the semiconductor wafer 22 may be removed from the etch tool 10, while preserving the vacuum in the etch tool 10. The semiconductor wafer 22 may be transferred from the etch tool 10 to a wet chemical bath 20 where the wafer may be subjected to aggressive chemicals to remove some of the residual sidewall passivation 25. EKC 265 and ACT 935 are examples of chemicals that are used in a wet chemical bath to strip residual sidewall passivation.
Wet chemical baths tend to be expensive to maintain. The consumed chemicals and environmental considerations in handling and disposing the chemicals also increase the cost of the chemical baths. As the amount of residue that is removed increases, the amount of chemicals consumed also increases.
Current etch tools, such as the TCP™ 9600PTX Metal Etch System available from LAM Research Corp. of Fremont, Calif., combine two inductively coupled plasma etch chambers with two microwave strip chambers. Each etch chamber requires a plasma source and each strip chamber requires a plasma source, which increases the cost and complexity of the etch tool. In the TCP™ 9600PTX Metal Etch System it is recommended that in the strip chamber the strip process be for 60 seconds for an oxygen nitrogen strip and the water vapor plasma corrosion passivation be for 30 seconds for a total process time of 90 seconds in the strip chamber.
The processing time in the etch tool and the wet chemical bath in the prior art comprises the sum of the etch time in the etch chamber, the etch mask strip time in the strip chamber, the corrosion passivation time in the strip chamber, transfer time between the etch chamber and the strip chamber, and time of residual sidewall passivation removal in the wet chemical bath. The transfer times between the two etch chambers and the two strip chambers increase processing time. In the prior art the time of residual sidewall passivation removal in the wet chemical bath could be about 20 minutes.
Since BCl3 reacts with oxygen to create a non-volatile residue, which will contaminate the etch chamber, it was typically thought to be desirable to keep oxygen out of an etch chamber that uses BCl3.
In view of the foregoing, it is desirable to provide an improved removal of residual sidewall passivation. It is also desirable to provide a less expensive etch tool. It is also desirable to increase the throughput of an etch tool.